Final answer:
Carbidopa, tolcapone, selegiline, and rasagiline are drugs that increase the duration of action of dopamine and/or the amount of levodopa that enters the brain.
Step-by-step explanation:
The drugs that increase the duration of action of dopamine (DA) and/or the amount of levodopa that enters the brain are carbidopa, tolcapone, selegiline, and rasagiline. These drugs work by different mechanisms to enhance the effect of dopamine in the brain.
Carbidopa is commonly used in combination with levodopa to treat Parkinson's disease. It inhibits the breakdown of levodopa in the periphery, allowing more levodopa to enter the brain and be converted into dopamine.
Tolcapone is another drug that inhibits the breakdown of dopamine, specifically by blocking the enzyme COMT. This leads to increased levels of dopamine in the brain.
Selegiline and rasagiline are selective inhibitors of MAO-B, which is an enzyme that metabolizes dopamine. By inhibiting MAO-B, these drugs increase the duration of action of dopamine in the brain.